This application claims the priority benefit of Taiwan application serial no. 89107841, filed Apr. 26, 2000.
1. Field of Invention
The present invention relates to a method of controlling a scanner. More particularly, the present invention relates to a method of controlling scanning discontinuity.
2. Description of Related Art
In the operation of a scanner, sometimes the scanning speed is faster than the data transmission rate to a host computer. To keep all the scanned data, a temporary storage area has to be allocated inside the scanner. This temporary storage area is known as a buffer. However, the rate of generation of data by a scanner is so fast that sometimes even the buffer is full. When the buffer is full, the scanner must stop scanning. Otherwise, some data are lost.
Conventionally, as soon as the buffer is full, the scanner will stop immediately. In other words, the chassis inside the scanner will stop. Scanning will resume only when the some of the data inside the buffer is emptied.
However, the chassis is moving forward and scanning at a constant speed before a request signal for stopping is sent to the driver of the chassis. After the chassis has stopped and a portion of the data in the buffer has transmitted, the scanner can resume scanning. Since the scanner is in a stationary state, the scanner needs to accelerate for awhile before picking up the normal scanning speed again. Consequently, the speed of movement of the chassis during this transition period is quite different from a normal scanning. In other words, there is a discontinuity in the middle of a scanning operation leading to a possible discontinuity in the scanned image.
In lower grade scanners, this type of problems are usually ignored leading to a break in the scanned image or discontinuity. However, in some higher-grade scanners, the chassis is allowed to move backward for a short distance before accelerating forward so that inertial effect of stopping and starting and other mechanical errors of the chassis itself are removed. In this type of scanners, when the chassis reaches the former stopping position, the chassis is already moving at the normal scanning speed. Hence, discontinuity of scanned image due to stopping is compensated. To deal with the problem, a conventional method relies on the arrangement proper timing of the chassis driver. Assume that a period t1 is required for the chassis to halt from a normal scanning speed. Moving backward for the chassis to halt from the normal scanning speed also requires the period of t1. Because of accelerating the chassis from a stop status to a status of the normal scanning speed in a forward or backward direction requires the same time periods, assuming that accelerating times are of the same for both directions, the accelerating times for both directions are also t1. In brief, total time spent to stop and restart a scanning operation is about 4t1, which comprising the time periods of decelerating from a constant forward speed to stop, moving backward to a constant backward speed, decelerating from the constant backward speed to stop, and accelerating forward to the constant speed.
The aforementioned description of the chassis is looked upon from a perspective of operational timing. From a mechanistic point of view, forces on the chassis and related components can be indicated by graphs shown in FIGS. 1A and 1B. FIG. 1A is a graph showing the variation of motor traction versus time for a conventional scanner in the process of stopping and restarting. FIG. 1B is a graph showing the variation of body extension versus time for a conventional scanner in the process of stopping and restarting. At time t=0, the forward-moving force provided by a motor is changed to an identical force in the opposite direction. After a period of 2t1, the amount of extension of the elastic body reaches a stable value. At this point, the chassis has retracted to a suitable position. The motor then provides a forward-moving force again. After another period of 2t1, the amount of body extension reaches a stable value. At this point, the chassis has reached a specified speed for scanning. In other words, the chassis returns to the former point where a signal for stopping has been issued at a constant forward speed. Consequently, scanning operation can be resumed without any image distortion or discontinuity.
However, each starting and stopping of the chassis requires a total delay of 4t1. Hence, scanning performance is greatly lowered.
Accordingly, one object of the present invention is to provide a controlling method capable of reducing scanning discontinuity in scanners. Since this invention targets the reason of discontinuity of scanning and controls the movement of the chassis, both scanning speed and efficiency of a scanner are improved.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for reducing scanning discontinuity. The method can be applied to control the movement of the chassis inside a scanner. During a reckoning period, a retracting force is applied to the chassis. At the end of the reckoning period, a forwarding force is applied to the chassis during a reversing period. At the end of the reverse period, no forces are applied within a stopping period. Finally, a forwarding force is applied to the chassis within another reckoning period.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.